The primary objective of the proposed research is to apply electrochemical techniques to the study of photo-sensitive chemical systems. Of particular interest are biological systems where rapid free-radical reactions are initiated by high-energy irradiation. The electrochemical measurements can be used simply to identify and monitor the concentration of free-radical and other transients, and to obtain kinetic data. In addition, the electrochemical characterization of relatively long-lived (greater than a few micro-seconds) excited species is proposed. Thus, the project must also involve the development of sensitive electrochemical techniques with micro-second time resolution for the detection and characterization of transient species. Another objective of the proposed research is to use electrochemical methods to simulate and study photo-induced reactions. That is, in many photochemical reactions the unstable intermediates are either oxidized or reduced forms, and may be generated electrolytically. Thus, with controlled potential electrolysis, chemical reactions can be initiated which are identical at least in part to those involved photochemically. In this manner a kinetics and mechanism study can be made under more favorable conditions, and conclusions can be transferred as far as applicable to the photochemical process.